The present invention relates to an electrical contact or electrode structure of a vaccuum interrupter.
Generally, a pair of electrical contacts or electrodes of a vacuum interrupter are disposed within a vacuum vessel through a pair of contact rods for selective contact with each other. The contacts are formed as substantially disk-shaped elements of copper or copper alloy, respectively. The mechanical strength of this electrical contact is relatively low since a plurality of slots or slits are provided in the contact.
Vacuum interrupters in which the aforesaid contacts are utilized are generally two types. One is a magnetic driving type that improves an interrupting performance by driving an arc utilizing a magnetic force. The other is an axial magnetic field type that improves interrupting performance by applying an axially oriented magnetic field parallel to an arc thereto, causing the arc to be dispersed in a stabilized manner to prevent concentration thereof. A typical magnetic drive type electrode of a vacuum interrupter is disclosed in U.S. Pat. No. 4,324,960 issued Apr. 13, 1982, wherein the electrode has a plurality of circular arc-shaped slots extending radially and circumferentially through a tapered portion of the electrode and terminating at a flat portion thereof.
The axial magnetic field type electrode of the vacuum interrupter is disclosed in U.S. Pat. No. 3,946,179 issued Mar. 23, 1976, wherein the electrode has a plurality of slits extending from the outer periphery thereof toward the central portion thereof.
Due to the number of slits or slots, both electrodes discussed supra wear easily and are not of long endurance because of the mechanical shock energy they are exposes to when placed between open and closed conditions. In either aforesaid type of electrode, in addition to the above-mentioned low mechanical strength of the electrical contact, the mechanical strength thereof is further lowered by annealing or brazing the contact rods to the contact elements. Further, in the electrode of the magnetic driving type vacuum interrupter, there are plural spiral slots defining electric arc segments likely to deform. With regard to the electrical contact of the axial magnetic field type vacuum interrupter, the electrical contact is provided with a plurality of slits formed radially for preventing an axially oriented magnetic field interlinks with the electrical contact; however, there occurs an eddy current in the electrical contact, resulting in a lowering of the interrupting performance. This construction also results in a lower mechanical strength.
Other prior art publications relevent to electrical contact/electrode structures of vacuum interrupters are as follows:
U.S. Pat. No. 3,592,987 discloses an electrode structure of a vacuum circuit interrupter comprising a disk of gettering material on the rear side of one or both of the separable contacts to absorb gas produced during opening and closing contact of the electrodes. The electrode structure consists of fibers of gettering material embedded in a matrix of material of good conductivity.
U.S. Pat. No. 3,614,361 discloses an electrode structure comprising a relatively flat disk made of high-cathode drop material, and spiral slots extending inwardly from the periphery of the contact filled with solid low-cathode drop material, facilitating arc rotation to effect arc extinguishment.
It is clear that these references are not directed to an improvement in a mechanical strength of the electrical contact or electrode, but solely teach electrode structures different from that of the invention which will be referred to later in greater detail.